It says:
"So if you had create a page title “Home” and you would now have two links to “Home” appearing in the navigation menu. Both links would also be going to the same location. Obviously you don’t want this."

This is exactly what happened (in my case one is called "Front Page" and the other "Apresentação".

But then it says:
"You can hide the second link by editing the page, and setting another page as the Parent in the Attributes module."

This doesn't work because this second page ("Front Page") doesn't show up in the dashboard) hence I can't make one the parent of the other.

Don't make it a child of "front page" make it a child of another page that you have created. That will hide one of the "front page" tabs. The other one will still remain and work to return visitors to your front page.